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<Technology Needs for Lake Management in Indonesia -
Investigation of Rawa Danau and Rawa Pening, Java>

D. Role of Rawa Pening

Initial investigation of Rawa Pening revealed that some assumptions commonly held about the lake were not accurate, and that it was desirable to clarify the general situation as regards the use of water and importance of water in Rawa Pening. The description below is an accurate statement of the general situation as found on investigation. It is against this background that further investigations of particular aspects of lake ecology and resource utilisation were undertaken.

1. Domestic use

In the Case Studies document (BPPT/UNEP, 1996) it is noted that ... "Rawa Pening has an important role in supplying drinking water for urban areas". This statement may reflect some misunderstanding. There is, actually, very little use of water form Rawa Pening for domestic purposes. There is some limited use of the water in incoming rivers on the shore the lake, before the rivers reach the lake. Water in the rivers is used for bathing and for washing clothes. Such areas usually have rock outcrops or substantial banks. The lake itself, being relatively shallow, has muddy shores for much of the year, and so does not lend itself to domestic use.

As the lake lies at the bottom of a former caldera and the surrounding land rises in some places, very steeply, and in other places, gradually, any water taken from the lake would have to be carried long distances to houses. There are no pumps to remove water from the lake to houses in the area, again because of the shallow nature of the lake and the seasonal variation in the amount of muddy shore exposed. The water has such a high bacterial content that it is, by WHO standards, unfit for swimming.

It is likely that the "domestic use for drinking water" mentioned in the Case Studies Document, refers to the use of bottled spring water, taken from springs which would otherwise flow into the lake. This is recorded below but cannot be seen as being lake water.

However, there is a network of pipes carrying water to houses in some of the villages on the shores of the lake. This water comes from springs and is generally of good quality. Such spring water is piped to houses, and is pumped or gravity fed. Springs which are at a lower level in the Tuntang valley than the lake (i.e. below the level of water in the outlet dam) may actually receive lake water, which has percolated through the ground, but this is uncertain.

These large springs are of considerable importance to the local community and water is pumped from them to villages in the area. Such springs cannot be considered as being Lake water.

There are other networks of pipes coming from check dams on rivers upstream from the lake. Water from these dams is used to provide water for irrigation of "padi" (rice) fields. Investigation suggests that little of the water from check dams is used domestically. It is noteworthy that such use of water from springs and check dams reduces the input of water to the lake.

Much of the water coming into the lake from villages and towns in the catchment has already been used domestically. The coliform count in the stream coming from Ambarawa has been reported to be outstandingly high.

Water from the Tuntang river is used many kilometres downstream. No information was available to the team on the quantity or quality of water drawn from the Tuntang River downstream, or exactly what it is used for, and this is not considered to be relevant to the present study which deals with the technological requirements for lake management.

2. Hydro-electric power generation

Water from the lake is used industrially in the generation of electric power. The power station is at Jelok (sometimes referred to as Jeklok) on the Tuntang river some kilometres below the outlet from the lake, but the holding dam at the outlet from the lake effectively controls the water level in the lake. If the holding dam did not exist, it is likely that the lake would not exist in its present form. The holding dam was constructed by PLN (Perusahaan Listrik Negara), the National Electricity Power Authority.

3. Industrial use of lake water

There is no evidence of any significant use of water from the lake for industry, other than for power generation.

4 Fisheries

There has been an important fishery on the lake. This has declined in significance in recent years, as the annual catch has declined. The reasons for the decline are not clear. The most obvious possible causes of the decline are pollution from a range of organic chemicals such as pesticides used on "sawah" (rice fields), pollution from fertilisers from irrigated sawah, overfishing by local residents, increasing eutrophication, and illegal use of poisons to catch fish.

The fishery has never been the main source of income for people living near the lake. The main source of income is from farming.

The fishery has provided a supplementary income for those people in local "kampungs" (villages) who are relatively poor compared to the others, and who do not own enough land to be able to grow enough food to meet their needs. The literature suggests that there may be a complex social reason based on recent history (Prajarta et al, 1979) why some villagers are forced to depend on the fishery for their income.

5. Recreation and tourism

The use of the lake for recreation is still on a very small scale. A few boats are available for hire for fishing on the lake, and the swimming pool at Muncul provides a focus for tourists as does the facility at Bukit Cinta.

However, during the last 10 years the tourist industry has grown significantly. This is likely to be an indication of future developments, which one might forecast as being the extension of hotels and restaurants along the slopes and shores of the lake, particularly near the main roads. This is coupled with the development of extensive parking areas and petrol stations, and increased soil erosion from heavily used bare ground. Tourists are likely to be mainly Javanese, and the facilities are at present designed to meet Javanese expectations.

6. Biological conservation

There is little of biological value in the area to merit preservation, in that sense of the word conservation. The original swamp forest which must have covered the area of the lake thousands of years ago has disappeared. A brief investigation of the shore of the lake near Ambarawa failed to reveal any trace of any remnants of swamp forest. The lake water itself is an example of a resource which merits conservation in the sense that it needs rational usage and management.

7. Irrigation

An extensive system of canals stretching for several kilometres has been constructed to provide water for irrigation for padi fields. The main development is south of Ambarawa. Much lake water is consumed in irrigation. There is no accurate measure of the amount involved.

8. Flood control

It has been claimed that Rawa Pening has an important role in flood control. This is not immediately apparent on investigation, as discussion with residents of low-lying areas of Ambarawa show that these are regularly flooded each wet season.

However, it appears that the capacity of Rawa Pening to hold back the crest of wet season flood waters saves areas downstream from extensive flooding. The investigators had no information on this and no way of assessing the relative areas which might be flooded under a particular set of conditions, as compared with the areas of towns near Rawa Pening which would be flooded under the same conditions. Such assessments would have to be based on the comparative financial and social impacts of flooding on those areas.

It appears that a policy decision has been made that Rawa Pening will be used for flood mitigation downstream in the Kabupaten. The economic bases for this decision as well as the origin of this decision are not known.

9. Transportation

The lake is not used at all for transport. In fact the abundant growth of water hyacinths on the surface would limit efficient use of the lake for transport.

10. Centre for scientific study

The complex and very obvious problems of Rawa Pening have already provided the basis for extensive research programs by the staff of Universitas Kristen Satya Wacana at Salatiga. Other research work has been carried out by staff from other institutions such as Universitas Indonesia and Universitas Gadjah Mada. In the past the UKSW developed a Research Centre at Bukit Cinta with basic laboratory facilities. This is apparently not functional at present, due to lack of supporting funds. The lake offers an ideal training ground for those who wish to take up lake management as a career. It also offers opportunities for the establishment of a permanent field studies centre for school education for children in the area.

The extensive research work carried out on Rawa Pening by staff, students, and visiting research workers from Universitas Kristen Satya Wacana, in Salatiga, led to the publication of numerous scientific and sociological papers. Many of these were written in Bahasa Indonesia and so received little circulation outside Indonesia. This research was carried out in the years prior to 1979. The papers provide a valuable insight into conditions in the lake at that time, and to the interaction between the villagers living on the shore and the environment of the lake itself. Many of these research papers were compiled into the massive 600 page report by Goeltenboth (1979) on the Rawa Pening Project. It is noteworthy that only one copy of this report could be found in Java. It was in the personal library of a member of staff of UKSW. No staff of Government Departments appeared to be aware of the existence of this research or of the document in question.

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